An attempt has been made to analyze immunologic mechanisms in EAE by in vitro examination of cells from BP-sensitized animals. It is well known that sensitized cells are stimulated to divide (proliferate) when they are exposed to specific antigen in vitro. Thus, cells from animals sensitized with BP in complete Freund's adjuvant (CFA) undergo proliferation in the presence of either BP or PPD. (CFA contains tubercle bacilli which sensitize the animal to PPD.) Our data on the stimulation of sensitized cells with specific antigen in vitro indicate that: 1) proliferation in culture in the presence of BP correlates well with the disease state, and 2) this proliferation is not induced primarily by the site on the molecule responsible for disease induction. The latter observation was somewhat surprising and led us to investigate other effects of antigen in vitro.